If you already own Widows 7 Home Premium, you have a full PVR/DVR in 'Windows Media Center'. An external tuner such as the SiliconDust HDHR is a very capable devise. It can be shown to have slightly lower performance than the best current tuner chips, but the difference is very small... manageable in all but the most extreme deep fringe applications. (Your situation is not 'deep fringe'.)
The HDHR works well with other operating systems also.
http://forum.tvfool.com/showthread.php?t=820
If you have trouble with High-VHF reception you can add a VHF antenna such as the Antennacraft Y5713, Y10713 or the Winegard YA1713. Use a UVSJ to combine the two antennas into a common coax down-lead.